The present invention relates to the manufacture of metal wire, rod, and the like, and in particular to apparatuses and processes for immersing a moving wire within a bath of molten metal such as zinc or lead, for the purpose of coating or quenching the wire.
Within the production of wire or metal rod (which will be referred to herein generically as xe2x80x9cwirexe2x80x9d), immersion of the wire within a bath of molten metal is required at one or more stages of production. For example, upon exiting the austinizing furnace the wire is quenched within a quench furnace. Conventionally, the quench furnace comprises a bath of molten lead or other metal, for rapidly cooling the hot wire from the furnace temperature of about 950xc2x0 C. to about 535xc2x0 C. Conventionally, a continuous length of wire is drawn from the furnace at a rapid rate, passes through the quench furnace and subsequently through various downstream processing means. These latter optionally include a coating station, in which the wire is coated by immersion into a bath of liquid metal such as zinc. Conventionally wire is drawn through the various stations in a generally horizontal direction.
Within conventional manufacturing processes, a molten metal immersion bath comprises a chamber or housing, in which the wire enters the housing at a level somewhat above the surface of the liquid metal, and is deflected downwardly into the liquid by means of an arrangement of sinkers or the like. The wire is subsequently directed back to a higher level to exit the chamber. The downward deflection is required in light of the difficulty in achieving a sealable opening within the chamber at a level below the surface of the liquid. To prevent leakage of the metal, the chamber must be fully sealed below the liquid surface level, thus necessitating within the prior art a tortuous path for the wire. The wire is drawn downwardly into the bath by the application of a relatively considerable downward force, in light of the high tension applied to the wire and the relatively high speed at which the wire is drawn through the fabrication stations. As a result considerable wear is typically experienced by the various sinker arrangements, as well as the wire handling equipment associated with drawing the moving wire through the tortuous path associated with immersion of the wire within a bath. Further, the wire itself experiences stress, leading to cracks, weaknesses and the like.
In order to prevent strain on the wire, leading to cracks, fractures, or weakened portions, it is desirable that the wire follow a generally straight linear path and any deflection from the horizontal be minimized.
It has been proposed to provide a wire coating station wherein the wire travels through the station without deflection from the horizontal. In particular, U.S. Pat. Nos. 3,956,537 (Raymond), 5,527,563 (Unger et al.) and 5,718,765 (Unger et al.) propose generally trough-like arrangements, with the wire passing through the trough in each case in a substantial horizontal direction without downward deflection. A coating layer is sprayed onto the wire as it passes through the trough, with a trough serving to contain the coating material in the regions surrounding the wire. However, this arrangement is not suitable for quenching hot wire exiting an austinizing furnace, as it does not fully immerse the wire within a bath, nor for a hot metal coating station requiring complete immersion within a molten metal bath.
There has not been prior to the present invention proposed any suitable arrangement for immersing wire within a bath of molten metal or the like, wherein the wire is conveyed through a bath in a substantially straight, horizontal, non-tortuous path.
The benefits that may be achieved by providing such an arrangement include:
improved metallurgical structures resulting from the lack of stress on the metal from the minimal distortion of the wire;
maintenance savings throughout the production line, as a result of avoiding the need for ceramic or metal sinkers, pulleys or the like for displacing wire downwardly into a bath;
reduction of strain on feeding and tensioning equipment, as a result of a more efficient passage of the wire through the molten metal baths, without the necessity of drawing a wire through displacement means;
reduction in manpower, production costs and scrap product, and increased speed of production and productivity as a result of the above.
As well, the overall length of the quench or coating stations may be reduced by application of the present invention, thereby further reducing costs associated with wire production.
In a further aspect, the molten metal within a conventional bath typically substantially circulates relatively slowly or not at all. As a result, a layer of laminar flow is created at the wire surface as the wire is drawn through the liquid at a high speed. This can result in localized fluctuations in temperature, wherein the liquid within the zone of laminar flow is elevated in temperature, resulting in a less efficient quenching or coating operation. More efficient coating and quenching processes may be achieved by imparting a velocity, and in particular a turbulent flow, to the molten metal within the bath, thereby minimizing the laminar flow effects. Further, improved processes may be achieved by directing a turbulent, relatively rapid flow in a direction countercurrent to the direction of travel of the wire within the bath. If the flow is imparted with sufficient velocity and turbulence, the laminar flow layer which normally surrounds wire drawn through a liquid bath is disrupted.
The present invention operates on the principle of providing within a molten metal bath a volume of molten metal that is elevated at a central region of the bath relative to the ends, thereby permitting the wire to pass through this elevated region in a straight path without downward deflection. The present invention also relies on a means for imparting a velocity to the molten metal within the bath, which conveniently is in a direction against the wire travel direction, and providing a degree of turbulence within the molten metal. The turbulence and the counterflow effectively disturb the laminar flow layer which normally surrounds wire traveling through a liquid bath, thereby increasing the effectiveness of the molten metal properties within a quenching operation or other stage requiring full immersion of the moving wire.
An object of the invention is to provide an improved apparatus and method for immersing wire within a liquid metal bath, for the purpose of annealing or coating the wire or other like purpose within a wire forming process. More particularly, the object is to immerse a moving wire within a bath, without downward deflection of the wire. In order to achieve these objects, the present invention provides an apparatus and method for immersing a moving wire within a molten metal bath wherein the liquid forms a hydraulic jump that effectively elevates a volume of the liquid within a standing wave configuration whereby a wire may be drawn in a substantially straight path through the standing wave.
It is a further object to provide an immersion bath characterized by a turbulent flow of molten metal in a direction against the wire travel direction, in order to effectively disrupt the layer of laminar flow adjacent to the wire, thereby improving the efficiency and efficacy of the immersion.
According to one aspect, the present invention comprises an apparatus for use in association with a wire forming arrangement, for immersing within a liquid metal bath a wire travelling in generally straight linear horizontal path, comprising;
an elongate tray having opposed ends and elongate sides, a flat floor, a dam at a second end of said tray and sidewalls along the side edges of the tray for maintaining a volume of liquid metal within said tray;
support means for supporting a wire at a height above said floor along a substantially horizontal plane;
a source of pressurized liquid metal, preferably comprising at least one pump means suitable for delivering a relatively high pressure and high volume stream of molten metal; and
a nozzle at a first end of said tray for directing the liquid from said source in a sheetlike flow along said floor towards said second end of said tray and over said dam, with sufficient velocity to generate by means of a hydraulic jump a standing wave of said liquid within said tray wherein the crest of said wave is at a level above said height thereby immersing a portion of said wire within said liquid at said standing wave.
In a preferred embodiment, the liquid is recirculated within the system. Further, the liquid cascades over the dam after contact with the wire into a reservoir pan, and is recirculated to the nozzle by a pump means or the like.
Preferably, the nozzle means comprises an elongate chamber communicating with the liquid source, having a slot-like outlet defined by spaced apart parallel plate means defining an inner space communicating with said chamber and opening onto the floor of the tray in a direction parallel to the tray floor. The slot-like opening has a height defined by the spacing of the parallel plate means and a width which in one aspect generally corresponds to the length of the chamber.
The relative dimensions and flow rate of the respective components and in particular the dimensions of the slot-like nozzle are an important aspect of providing a suitable hydraulic jump within the tray. The spaced apart parallel plates in the nozzle means of the preferred version have a spacing therebetween of about 6 mm , and a width of about three feet and said source of liquid metal is adapted to provide said metal at a pressure of between 22 psi and 30 psi at a flow rate of about 110 kg/sec. of molten lead. Within these parameters, the resulting velocity of the lead exiting the nozzle is between about 10 and 15 ft/sec. In general terms in one aspect of the invention, the slot dimensions and the liquid flow rate that achieve a suitable hydraulic jump conforms to the following formula:   D  =            d      2        ⁡          [                                    1            +                                          8                g                            ⁢              x              ⁢                              xe2x80x83                            ⁢                                                Q                  2                                                                      L                    2                                    ⁢                                      d                    3                                                                                      -        1            ]      
where D=wave height
d=slot height (distance xe2x80x9cxxe2x80x9d)
g=gravitational constant
Q=flow rate
L=slot width (distance xe2x80x9czxe2x80x9d)
It is understood that depending on the selected speed at which the wire array is drawn through the apparatus and the desired immersion time, the slot dimension and flow rate parameters will be selected according to the above formula to achieve a suitable height D of the standing wave. Preferably, D is selected to achieve a minimum six second immersion of a wire array drawn through the apparatus.
The invention comprises in a further aspect:
a pressurized source of molten metal;
a tray having a substantially flat floor, first and second opposed ends, elongate
opposed sides and sidewalls along the side edges;
a nozzle at a first end of said tray communicating with said pressurized source, for directing a stream of said liquid onto the floor of said tray, in a sheet like flow towards an opposed second end of said tray;
wire entry and exit means within said tray permitting wire to be drawn through said tray in a straight, linear generally horizontal path from said second end to said first end thereof, substantially parallel to said floor and at a height elevated above the floor;
molten metal recirculating means for removing said liquid from said second end of said tray and recirculating said liquid to said pump means;
whereby said pump means are adapted to pump the molten metal through said nozzle with sufficient velocity to create a hydraulic jump whereby a standing wave is created of said liquid of sufficient height to fully immerse a portion of the wire within the molten metal, with the liquid within the standing wave characterized by a relatively turbulent flow of said liquid in a direction against the direction of travel said wire passing through said tray.
In a further aspect, the invention comprises a method for immersing a wire within a bath of molten metal, comprising the steps of:
providing an elongate tray having opposed ends and elongate sides, a flat floor, a dam at a second end of said tray and sidewalls for maintaining a liquid metal within said tray;
providing a volume of liquid coating metal within said tray having a surface at a first height;
support means for supporting the wire at a second height above said first height along a substantially horizontal plane;
a source of pressurized liquid metal such as a pump means; and a nozzle at a first end of said tray;
drawing the wire above the floor of the tray in a generally horizontal, straight path at the second height;
directing said liquid from said source in a sheetlike flow along said floor towards said second end of said tray and over said dam, with sufficient velocity to generate a hydraulic jump consisting of a standing wave of said liquid within said tray wherein the crest of said wave is at a level above said height to substantially immerse said wire within said liquid at said standing wave; and
receiving said liquid flowing over said dam and recirculating said liquid into said source.
Although within the preferred embodiments of the invention the wire is drawn axially relative to the elongate axis of the wire, it is contemplated that with suitable modifications the invention may operate in connection with a transverse movement of the wire.
Having briefly characterized the salient features of the present invention, a detailed description of a preferred embodiment will now be described. Further aspects of the invention will become apparent within the following detailed description.